The bulk physicochemical and organoleptic properties of emulsion-based food products are ultimately determined by the concentration, dimensions, interactions, and dynamics of the various types of structural entities present within them (e.g., atoms, molecules, molecular aggregates, crystals, micelles, droplets, air bubbles, and individual phases) (Figure 1.8). The
* It should be noted that the continuous phase of an emulsion is also capable of melting or crystallizing, which can have a profound influence on the overall properties. For example, the characteristic texture of ice cream is partly due to the presence of ice crystals in the aqueous continuous phase, whereas the rheology of butter and margarine is determined by the existence of a network of aggregated fat crystals in the oil continuous phase.
properties of emulsions can therefore be studied at a number of different levels of structural organization (e.g., subatomic, atomic, molecular, supramolecular, colloidal, microscopic, macroscopic, and organoleptic) depending on the concerns of the investigator (Eads 1994). Subatomic particles interact with each other via strong and weak nuclear forces to form atoms. Atoms interact with each other via covalent and ionic bonds to form molecules. Atoms and molecules interact with each other via various covalent and noncovalent forces to form separate phases (which may be gas, liquid, or solid), simple solutions, molecular aggregates, and colloidal particles (Chapter 2). The bulk physicochemical and organoleptic properties of an emulsion depend on the way these structural entities interact with one another to form the emulsion droplets, interfacial region, and continuous phase. A more complete understanding of the factors that determine the properties of emulsions depends on establishing the most important processes that operate at each level of structural organization and linking the different levels together. This is an extremely ambitious and complicated task that requires many years of painstaking research. Nevertheless, the knowledge gained from such an endeavor will enable food manufacturers to design and produce higher quality foods in a more cost-effective and systematic fashion. For this reason, the connection between molecular, colloidal, and bulk physicochemical properties of food emulsions will be stressed throughout this book.
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